This invention relates to polyphenylene ether resins, and more particularly polyphenylene ether formulations with improved flow.
Polyphenylene ether resins (PPE) are an extremely useful class of high performance engineering thermoplastics by reason of their hydrolytic stability, high dimensional stability, toughness, heat resistance and dielectric properties. They also exhibit high glass transition temperature values, typically in the range of 150xc2x0 to 210xc2x0 C., and good mechanical performance. This unique combination of properties renders polyphenylene ether based formulations suitable for a broad range of applications, which are well known in the art. One example is injection-molded products, which are used for high heat applications. Polyphenylene ether polymers typically have relatively high molecular weights and possess high melt viscosity with intrinsic viscosity values typically greater than about 0.4 dl/g as measured in chloroform at 25xc2x0 C.
One area in which polyphenylene ether based compositions has required an improvement is melt flow capability, i.e. the ability to flow freely at elevated temperatures during various processing stages such as extrusion and molding. Poor melt flow can impact the size and type of the part which can be prepared with the composition and influence the type of equipment in which the composition is processed. In U.S. Pat. No. 4,154,712 to G. Lee Jr. teaches that processability can be improved by decreasing the molecular weight of the polyphenylene ether polymers; however, lower molecular weight sometimes adversely affects other properties such as impact strength. To aid processing, polyphenylene ether resins are often prepared with flow promoters, such as polystyrene, saturated polyalicyclic resins and terpene phenol to reduce viscosity and impart high flow to the resulting composition. Polystyrene, terpene phenol and other such flow promoters reduce the heat deflection temperature (HDT) of the product and typically increase the flammability of the PPE resin, as measured under UL94 standard protocol.
Efforts to improve the flow characteristics of PPE resins with minimal or no loss of HDT values and impact other properties have been made. For example, U.S. Pat. No. 5,081,185 to Haaf et al. describes compositions comprising a blend of two or more polyphenylene ether resins with one resin having high intrinsic viscosity values of at least about 3.8 dl/g and the other having low intrinsic viscosity values of no greater than 0.33 dl/g. The blend of the two PPE resins exhibits higher melt flow with no substantial decrease in heat deflection temperature (HDT) when compared to the high intrinsic viscosity PPE resin of the blend. In addition, U.S. Pat. No. 5,376,724 to Bailey et al. discloses polyphenylene ether compositions, which contain a resinous additive that improves flow with only minor reductions in HDT values and impact strength. The resinous additive is said to comprise vinyl aromatic monomers such as sytrene monomers or a hydrocarbon compound containing at least 35 wt % aromatic units.
It is desirable to provide a PPE resin formulation with high flow characteristics with reduced loadings of flow modifier to minimize the impact on HDT values, impact properties and flame retardance.
The present invention provides blends of polyphenylene ether resin, and dendritic polymers. It has been discovered that substantially equivalent improvements in the flow properties of compositions containing polyphenylene ether resins can be obtained with smaller amounts of dendritic polymers when compared to conventional flow modifying additives.